Direct manufacture of powdery calcium cyanamide



May 12, 1959 F. J. KAL-tss ET AL 2,886,417

DIRECT MANUFAGTURE OF POWDERY ,CALCIUM CYANAMIDE Filed Feb. 18. 1954 DIRECI MANUFACI'URE OF POWDERY CALCIUM CYANAIVIIDE Franz J'. Kness, Thomas Fischer and Franz Gtzinger, Trostberg, and Hermann Kronacher, Feldkirchen, near Trostberg, Germany, assignors to Suddeutsche Kalkstickstot-Werke A.G., Trostberg, Bavaria, Germany .Application February 18, 1954, No. 411,218

' 6 Claims. (Cl. 2&279)

The invention relates to process and apparatus for preparingvcalcium cyanamide from calcium carbide andnitrogen.

For the continuous preparation of calcium cyanamide,'

it has already been proposed to react the starting materials in a rotary kiln.- However, it was found that the mass, irrespective of the particle size of the starting materials, had a strong caking tendency, and that the reaction product had to be subjected to an after-treatment in order to render it suitable for commercial use.

lt `has also been proposed to provide bathe rings in the rotary kiln so as to concentrate the reaction products which surround and dilute the calcium carbide in the course of the reaction. Such concentration by means of baie rings, however, does not give the desired results because segregation takes place due to the uniform rotation of the kiln and to the diterent gravities of the calcium cyanamide and carbide. The reaction product, i.e. the calcium cyanamide, which is lighter, concentrates on top of the concentration zone and impedes or completely prevents the access of nitrogen to the underlying carbide.

It is a principal object of this invention' to provide a method and apparatus for the continuous manufacture of powdery calcium cyanamide, which avoid the recited drawbacks.

Other objects and advantages will become apparent from a consideration of the specification and claims.

The apparatus according to the invention comprises a rotary drum, in which the baie ccct is accomplished by an enlargement at the feed end of the drum, whereby the axis of said enlargement forms an angle with the axis of the drum. It is of particular advantage to provide an enlargement which flares towards the exit end of the drum.

The invention will be well understood from the following description of certain illustrative embodiments thereof shown by way of example in the accompanying drawings, wherein:

Fig. I is an elevational section, showing one embodiment of the invention, and

Fig. 2 is a section similar to Fig. 1, showing a modified construction of a rotary drum according to the invention.

It will be understood that the views of the drawing are purely diagrammatic.

i.e. calcium cyanamide, preferably in powdery form,

Referring now to the drawings, like numerals identify i similar parts, and, as will be seen, the kiln consists of a metal cylinder 1 provided with a refractory lining Z, enclosing a chamber 3. The kiln is mounted horizontally, preferably with a slight inclination of about 2 towards the exit end; it is rotated in races 7 and 8 and is driven by the annular gear 9. Near to one end, said chamber 3 is widened to an enlargement 4, the axis of which forms an angle with the axis of the chamber 3, and which allows concentrating or accumulating of the charged material. Calcium carbide, or a mixture of calcium carbide with calcium cyanamide, is fed into said enlargement 4 by a screw conveyor 5. Prior to the operation of the kiln, the enlargement 4 is filled with the reaction product,

and heated. Instead of employing calcium cyanamide, the enlargement may be filled With'another substance which does not take part inthe reaction. Fori'stance, the enlargement can be filled with carbon dusrtgwhich does not burn on heating because of the exclusion of Nitrogen is admitted through the tube 6.

In the enlargement 4, the introduced bed of calciumcyanamide or other inert substances is intimately mixed with the calcium carbide charge, which mixing operation is assisted by the angular relationship between 4theaxis of the enlargement '4 and .the kiln axis. Due to the presence of a large amount of calcium cyanamide or other inert material, the carbide concentration is relatively low ing in spite of the high temperatures'. v

The continuously charged calcium carbide is converted and the temperature high, which conditions prevent calc# to at least percent into calcium cyanamide, so that during the course'of the process the bed consists of about 80 percent of calcium cyanamide.

If the carbide charge is mixed with calcium cyanamide, such calcium cyanamide has not the function to modify substantially the carbide concentration in Athe calcium cyanamide bed in the enlargement 4; saidcalciurn cyanamide is admixed only in'order to control the'tempera" tureand to'cnsure that a'predctcrmined teni-1' perature is not-exceeded. The optimum reaction 'temperature is in the range of about 1000 to 1100 C.

For a daily production of 70 tons (metric) we use a rotary kiln, which has a diameter of about 2 m. and a length of about 14 m. of which 3 m. are taken up by the enlargement 4 and I1 m. by the chamber 3. The diameter of the enlargement is about 1.2 to 1.5 times that of the chamber and the axis of the enlargement and chamber form an angle of about 5 to 7 degrees.

This rotary kiln is operated in such a way that it is first filled with the inert material, preferably powdered calcium cyanamide, then heated to reaction temperature, and subsequently charged with powdered calcium carbide while nitrogen is passed into the When 60% @C2 is used, we adjust the rate of -rotation of the kiln and the Vrate' of travel therethrough in such a way that about 93 to percent of the carbide is nitrogenated in the enlargement 4 within about l hour; subsequently the m'trogenation is completed in the chamber 3 to a product which contains not more than about 0.1% of residual carbide. During the nitrogenaton, the calcium carbide is at all times so much diluted with calcium cyanamide as to prevent overheating and caking.

With the described rotary kiln, it is possible to use powdery carbide as starting material and powdery calcium cyanamide as ller and to obtain directly a powdery end product, which can be marketed in this form for use, for instance, as a herbicide. As it is well known in order to be effective as a herbicide, calcium cyanamide must be employed as a` powder.

The rotary kiln of the invention may be used for intermittent or continuous charging, and it will be obvious that details of the described apparatus and method herein set forth may be varied within comparative wide limits without departure from the essential features of the invention.

We claim:

1. A rotary kiln suitable for the manufacture of calcium cyanamide comprising a rotary drum having a. feed end and a discharge end, the feed end of said drum forming an enlargement having at its juncture with the discharge end a larger inner diameter than said discharge end, thus providing a retaining edge for the charge on its travel from the feed end to the discharge end, the center axis of said enlargement forming an angle of about 5 to 7 degrees with the center axis of said dis- Patented May 12, 1959 of the drum,` means toV feed calcium carbide into the feed end of said drum, and meansbto admit nitrogen into said drum. f.

' 2. A rotary drum .as denedfin, claismY l-wherein--the ratio of the-diameters of said enlargement and said-dis charge end isaboutf. llto 115:1.-

3. Av rotary kiin for the manufacture of calciurncyanamide comprisingarotary drum having a Afeedv end and adischarge'end, the feed end of said- .drum an'ng in.- the direction of the discharge end having at the junction. with said discharge end a larger' inner diameter than said discharge end, thus forming a retaining edge for the chargev traveling through the drum, the center axis of saidfeed end. forming an angle ofabout 5 to 7 degreeshwith the center axis of said discharge end, which latter axis defines the axis of rotation oi the drums-means to'feed calcium carbide into: the fe'ed end. ot said drum, and rueansfto-aclmit nitrogen into-'said-.drum. t l

4. A rotar'y kiln for thedirectmanucturepipowdety'. calcium cyanarnide from powdery calcium carbidleicomprising two immediately-adioining reactionf chambers.- of diierent cross section, the irstfreaction chamber .having at the junction of said chambers.-adiameterabout 1.2 to 1.5 times larger than the diameter o f the-second reaction chamber and forming. aretaining edgeffor thecharge at the. junction with said second. reactionchamberg, saidldxst reaction chamber being arrangedfor a'-charge of powdery calcium carbide-until. about-80 percent there-- of have been nitrogenated, s aidfdseeonch reaction chamber having` at least twice the length o 'fsaid first reactioncham- '4 ber-and being'arraged for completing' the nitrogenation of the calcium carbide delivered from said rst reaction chamber, the center axis of said second reaction chamber defining the axis of rotation of the kiln and the center axis 0f said rst reaction chamber being inclined against the center axis of said secondreaction chamber by an angle of about 5 to 7 degrees.

5. Arotary/Akiln as defined in c1 1, wherein at the junction of the feed end and the discharge end the inner circumference of the feed end is eccentric to the inner circumference of the discharge end.

6. A -rotary kiln-having at its feed end an extension of larg'er' diameter than the' diameter of the kiln, the center axis of said extension forming an angle of about 5 to 7 degrees` withv the axis of rotation. of the drum, said axis of rotation being coincident with the center axis of the drum, means to feed a' charge into said extension, said charge advancing on rotation of said drum in a forward and backward motion through. said. extension clue to said angular relationship .of the center axis of the extension to the axis of rotation, and means to withdraw the charge from the-drum.

`References Citedv inthele of this patent STATES PATENTS 1,337,750 Carlson Apr. 20, 1920 2,180;382 Winter et al. Nov. 21, 1939 2,259,702' Liudliord Oct. 2l, 1941 f 2,352,0'51A Wendlandt et al. June 20, 1944 

1. A ROTARY KILN SUITABLE FOAR THE MANUFACTURE OF CALCIUM CYANAMIDE COMPRISING A ROTARY DRUM HAVING A FEED END AND A DISCHARGE END, THE FEED END OF SAID DRUM FORMING AN ENLARGMENT HAVING AT ITS JUNCTURE WITH THE DISCHARGE END A LARGER INNER DIAMERTER THAN SAID DISCHARGE EDN, THUS TRAVEL FROM THE FEED END TO THE DISCHARGE END, THE ITS TRAVEL FROM THE FEED END TO THE THE DISCHARGE END ATHE CENTER AXIS OF SAID ENLARGEMENT FORMING AN ANGLE OF ABOUT 5 TO 7 DEGREES WITH THE CENTER AXIS OF SAID ROTATION CHARGE END, WHICH LATTER AXIS DEFINES THE AXIS OF ROTATION OF THE DRUM, MEANS TO FEED CALCIUM CARBIDE INTO THE FEED END OF SAID DRUM, AND MEANS TO ADMIT NIRTOGEN INTO SAID DRUM. 